1. Field of the Invention
The invention relates to a control device and control method for a vehicle on which an internal combustion engine that serves as a driving force source is mounted.
2. Description of Related Art
A vehicle on which an internal combustion engine that serves as a driving force source is mounted is generally equipped with an oil pump that is driven by driving force from the internal combustion engine, and driver's operation is assisted through power steering, brake assist, or the like, by hydraulic pressure generated by the oil pump. In such a vehicle, when an engine stall occurs while travelling, the oil pump stops, and assist operation, such as power steering and brake assist, is stopped, so driving operation is problematically influenced. Then, the vehicle that travels using driving force from the internal combustion engine includes a control device that executes engine stall prevention control for preventing occurrence of an engine stall.
There is known a control device of this type (for example, see Japanese Patent Application Publication No. 2010-180987 (JP 2010-180987 A). When a vehicle speed increases in a direction opposite to a specified range in a state where an accelerator pedal is not depressed on an uphill and then the engine rotation speed of an internal combustion engine has decreased, the control device shift the inside of a transmission into an interlock state to restrict movement of a vehicle.
The control device described in JP 2010-180987 A is applied to the vehicle on which the internal combustion engine and the automatic transmission are mounted. Then, when neither the accelerator pedal nor a brake pedal is depressed on an uphill, and when the vehicle speed increases in a direction opposite to a specified range and, as a result, the engine rotation speed has decreased at a rate of change higher than or equal to a predetermined value, the control device determines that an engine stall is likely to occur. Then, the control device changes engagement states of a plurality of frictional engagement elements of the automatic transmission, and shifts the inside of the automatic transmission into an interlock state to stop the vehicle.
In addition, there is known a control device (for example, see Japanese Patent Application Publication No. 2010-96051 (JP 2010-96051 A). When a vehicle has travelled in a direction opposite to a specified range, the control device increases power output from an engine to restrict a change of a vehicle speed.
The control device described in JP 2010-96051 A, for example, increases an engine torque to restrict a rate of increase in vehicle speed in a direction opposite to a specified range in a situation that, while travelling on a narrow uphill, the vehicle and an oncoming vehicle cannot pass each other and the vehicle is reversed to a passing place, a driver does not change the specified range but only releases a brake pedal to intentionally reverse the vehicle in the opposite direction. Then, when the vehicle speed in the opposite direction has reached a predetermined value, the control device further increases the engine torque to keep the vehicle speed constant.
However, when the above-described control device described in JP 2010-180987 A determines that the vehicle starts travelling in a direction opposite to a specified range, the control device establishes an interlock state inside the automatic transmission to stop the vehicle, but the control device does not allow the vehicle to travel in the direction opposite to the specified range.
In addition, the control device described in JP 2010-96051 A restricts the vehicle speed or the rate of increase in the vehicle speed when the vehicle starts travelling in a direction opposite to a specified range, so the flexibility of adjustment of the vehicle speed by a driver is limited. That is, in the case where the driver desires to cause the vehicle to quickly travel in an opposite direction as well, the vehicle speed or the rate of increase in the vehicle speed is restricted, the vehicle may not reverse at a desired speed or it may take a time until the vehicle reaches a desired vehicle speed. Furthermore, the control device described in JP 2010-96051 A controls the engine torque on the condition that the brake pedal is released, so, for example, the driver is problematically not able to cause the vehicle to travel in an opposite direction at a desired speed while adjusting a depression amount of the brake pedal. As a result, the vehicle may not be reversed at a vehicle speed intended by the driver.
Therefore, both the control devices described in JP 2010-180987 A and JP 2010-96051 A are not able to freely adjust the vehicle speed in response to the condition of a travelling road, such as the width, gradient or curvature of an uphill or downhill, a presence of another surrounding vehicle, or the like, when the driver intentionally causes the vehicle to travel in a direction opposite to a specified range. Thus, both the control devices described in JP 2010-180987 A and JP 2010-96051 A are configured to prevent an engine stall; however, the behavior of the vehicle intended by the driver is not achieved, so drivability may deteriorate.